The present invention relates to an organic electroluminescent device, and more particularly, to an organic electro-luminescent display and a fabrication method thereof.
Organic electroluminescent devices have the characteristics of thin profile and light weight, and the advantages of self luminescence, high luminescent efficiency and low driving voltage. In accordance with organic luminescent materials, organic electro-luminescent display devices can be molecule-based devices or a polymer-based devices. The molecule-based device, called an organic light emitting display (OLED), uses dyes or pigments to form an organic luminescent thin film. The polymer-based device, called a polymer light emitting display (PLED), uses conjugated polymers to form an organic luminescent thin film.
Typically, a conventional organic electroluminescent device, for example an OLED, includes a glass substrate with an anode layer, a hole-injecting layer, a hole-transporting layer, an organic luminescent material layer, an electron-transporting layer, an electron-injecting layer and a cathode layer sequentially formed on the glass substrate. The hole-injecting layer, the hole-transporting layer and the organic luminescent material layer are generally referred to a luminescent layer. Typically, the anode layer is formed of indium tin oxide (In2O3:Sn, ITO) which has the advantages of facile etching, low film-formation temperature and low resistance. When a bias voltage is applied to the OLED, an electron and a hole passing through the electron-transporting layer and the hole-transporting layer respectively enter the organic luminescent material layer to combine as an exciton and then release energy to return to ground state. Particularly, depending on the nature of the organic luminescent material, the released energy presents different colors of light including red light (R), green light (G) and blue light (B). Normally, the light is emitted from one end of the substrate adjacent to the anode layer.
Normally, the cathode layer employs highly reflective material to increase luminescent brightness. The reflection of ambient light passing through the anode layer and entering the OLED by the cathode layer is, however, also increased. Thus, intensity of the reflected lights may be greater than that emitted by the OLED when operating either indoor or outdoor under bright conditions. Thus, image contrast of the OLED suffers and images cannot be clearly presented.